The present invention generally relates to an implantable cardiac stimulation device. The present invention more particularly relates to such a device, which automatically adjusts inter-chamber pacing delay to optimize pacing effectiveness.
Implantable cardiac stimulation devices are well known in the art. Such devices may include, for example, implantable cardiac pacemakers and defibrillators either alone or combined in a common enclosure. The devices are generally implanted in the pectoral region of the chest beneath the skin of a patient within what is known as a subcutaneous pocket. The implantable devices generally function in association with one or more electrode carrying leads, which are implanted within the heart. The electrodes are positioned within the heart for making electrical contact with their respective heart chamber. Conductors within the leads couple the electrodes to the device to enable the device to deliver the desired therapy.
Traditionally, therapy delivery had been limited to the right side of the heart. However, new lead structures and methods have been proposed and even practiced for also delivering cardiac rhythm management therapy from or to the left heart. These lead structures and methods provide electrode electrical contact with the left atrium and left ventricle of the heart by lead implantation within the coronary sinus of the heart. As is well known, the coronary sinus passes closely adjacent the left atrium, extends into the great vein adjacent the left ventricle, and then continues adjacent the left ventricle towards the apex of the heart.
It has been demonstrated that electrodes placed in the coronary sinus and great vein may be used for left atrial pacing, left ventricular pacing, and cardioversion and defibrillation. These advancements enable implantable cardiac stimulation devices to address the needs of a large patient population from those which would benefit from right heart side pacing alone to those which would benefit from left heart side pacing in conjunction with right heart side pacing (bi-chamber pacing), to those which would benefit from left heart side pacing alone.
For example, the potential of multi-site pacing to improve the hemodynamic status of select patient populations is well established in the research community. One area of active research is in determining the optimal ventricular pacing configuration. For example, the results of one study suggest that optimal results are obtained by pacing on the side of the heart that has the conduction delay, so that left ventricular pacing gives superior performance for patients with a left bundle branch block, while right ventricular pacing yields better results in patients with right bundle branch block. As illustrated by those who conducted this study, the problem is typically couched in terms of pacing mode, so that comparison is made among right ventricular pacing, left ventricular pacing, and simultaneous bi-ventricular pacing. Unfortunately this approach considers only a small subset of the parameter space, and therefore carries the very real risk of missing altogether the optimal pacing configuration.
Multi-site pacing has further challenges. One such challenge is identifying the optimal pacing site. This challenge is complicated by the fact that only a limited region of the left ventricle is accessible for pacing, particularly when access is obtained via the coronary venous system.
An additional challenge in multi-site pacing is that the optimal pacing configuration is dependent on the physiologic state of the patient. In patients with Hypertrophic Obstructive Cardiomyopathy, for example, the degree of obstruction is dependent on posture. Thus, the optimal pacing configuration is likely to change with changes in posture. For example, the optimal configuration for an unsedated, walking patient is likely to be different from what is optimal for a patient who is sedated and supine on the examination or operating table.
The optimal pacing configuration may also change as the patient""s myocardial state changes. Myocardial remodeling is associated with the progression or regression of heart failure. Such remodeling may depend on response to therapy, lifestyle changes, and age. As the heart remodels, the optimal sequence of activation may change. For example, in the acute phase of pacemaker implantation, left ventricular pacing may have been optimal for a given patient. Over weeks or months, the heart may remodel such that more synchronous bi-ventricular pacing becomes optimal.
The present invention provides an implantable cardiac stimulation device and method which optimizes pacing effectiveness by effectively selecting a pacing configuration within a continuum of pacing configurations ranging from right chamber pacing alone, to simultaneous right and left chamber pacing, to left chamber pacing alone. In accordance with the present invention, this is accomplished by selecting an inter-chamber pacing delay ranging from a delay which captures only a right chamber of the heart, to no delay for synchronous bi-chamber pacing, to a delay which captures only a left chamber of the heart responsive to a sensed parameter associated with pacing effectiveness.
In accordance with the present invention, a pulse generator delivers right and left pacing pulses to corresponding respective right and left chambers of the heart. The corresponding right and left chambers may be, for example, the right and left ventricles or the right and left atria. The right and left pacing pulses are delivered with a selected pacing delay therebetween which delay is within a continuum from left chamber pacing alone, to simultaneous right and left chamber pacing, to right chamber pacing alone. A sensor, such as a ventricular pressure sensor, which senses ventricular pressure associated with hemodynamic output, provides a pulse amplitude. A control circuit selects the pacing delay which provides the maximum pulse amplitude. In this manner, a pacing delay is selected which optimizes the mechanical efficiency of the heart.
In accordance with a preferred embodiment, the control circuit includes a processor. The processor is programmed to initiate a pacing delay selection and to cause the pulse generator to vary the pacing delay with successive cardiac cycles until a maximum in the sensed parameter is obtained. The processor may continuously initiate the pacing delay selection or may initiate pacing delay selection at spaced apart times or when the patient changes posture.
The present invention thus enables bi-chamber pacing to be amenable to continuous hemodynamic performance maximization even as physiologic state changes. It further obviates the need for optimized electrode placement as, for example, a left ventricular pacing site, by compensating for a sub-optimal electrode placement.